Ion trap of uniform flux density



June 3, 1952 D. P. INGLE ETAL 2,598,916

ION TRAP OF UNIFORM FLUX DENSITY Filed Aug. 11, 1951 FLUX DENSITY- ffiuelzfom" flow/a 1%:1/ Izzy/e 50/ l- Fez'c/rey Patented June 3, 1952 14 UNITED STATES PATENT OFFICE ION TRAP OF UNIFORM FLUX DENSITY Donald Paul Ingle, Defiance, and S01 L. Reiches, Cleveland, Ohio, assignors to All Star Products, Inc., Defiance, Ohio, a corporation of Ohio Application August 11, 1951, Serial No. 241,458

Our invention relates to an improved ion trap to fit on the neck of a cathode ray tube and capable of creating a substantially uniform magnetic flux density over the neck of the tube.

It is common practice in cathode ray tubes, particularly those intended for television use, to orient the electron gun in tilted relation to the axis of the tube. A magnetic ray beam deflecting device is placed over the neck of the tube and acts to deflect the electrons from the tilted path of travel to the desired path coaxial with the tube. Ions, however, are not substantially deflected and consequently travel harmlessly to strike a suitable barrier plate. In this fashion the reduction in screen life, otherwise attendant the presence of ions in the ray beam, is avoided.

When the above mechanism is used with electrostatically focused cathode ray tubes, the ion traps heretofore available are exceedingly critical in adjustment and may be wholly inoperative. Such traps also introduce an intolerable degree of ray beam defocusing or astigmatism with electrostatically focused tubes. This eflect appears to be due to the characteristics of the cylindrical focusing lens used in electrostatically focused cathode ray tubes. 7

In accordance with the present invention this difliculty is overcome and a non-critical ion trap providedfor electrostatically focused cathode ray tubes. This trap is characterized by the ability to produce a substantially uniform magnetic flux density over the cross-section of the tube neck and has been found to be highly efiective in separating the electron ray beam from the ions without critical adjustment and also without defocusing or astigmatism.

It is therefore a general object of the present invention to provide an improved ion trap for a cathode ray tube characterized by a uniform flux density.

Another object of the present invention is to provide an ion trap characterized by uniform flux density that is simple and inexpensive in construction, reliable in operation, non-critical as to adjustment, and is inherently suitable for use with electrostatically focused television receiver tubes.

Still another object of the present invention is to provide an improved ion trap suitable for use with an electrostatically focused cathode ray tube.

The novel features which we believe to be characteristic of our invention are set forth with particularity in the appended claims. .Our invention itself, however, both as to its organiza- Claims. (Cl. 313-75) tion and mode of operation, together with further objects and advantages thereof, will best be understood by reference to the following description taken in connection with the accompanying drawings, in which:

Figure l is a fragmentary side elevational view of the trap of the present invention mounted on the neck of a cathode ray tube;

Figure 2 is a cross-sectional view through axis 2-2, Figure 1, but omitting the ray beam producing and deflecting elements of the cathode ray tube; and

Figure 3 is an illustrative chart, drawn to the same scale as Figure 2, showing the variation in flux density along the axis X--X, Figure 2, as the shunt is moved along that axis.

Referring now to Figure 1, there is shown at in a fragmentary portion of the neck of a cathode ray tube. The tube includes an electron gun I2 comprising a heated cathode and electron accelerating and beam forming elements adapted to produce a ray beam oriented at a slight angle in relation to the axis of the tube. The tube also includes a ray beam focusing mechanism and means to deflect the ray beam to impinge upon the fluorescent tube screen at desired points, such as the scanning raster of a television system.

In the type of cathode ray tube to which the present invention is particularly applicable, the ray beam focusing means consists of a cylindrical focusing electrode l4 having one or more apertures concentric with the neck of the tube, to

which is applied biasing potential of preselectedv value to cause the electrons to converge on the tube face or screen.

The electron gun I! has an end plate with a small aperture concentric with the neck of the tube and through which the electron beam should pass. The beam produced by the electron gun is directed in tilted relation to the axis of the tube so that the undeflected beam strikes the edges of the plate and does not pass through the aperture. The electrons in the beam are deflected so as to pass through the aperture by the ion trap, indicated generally at I6, Figures 1 and 2.

The trap consists of a pair of straps, I8 and fill, of soft iron or similar magnetic material. These straps are complementary to each other and, in regions la and 20a, are arcuate in shape to conform to the curved outer surface of the neck of the tube where they overlay a substantial portion of the neck to define opposed magnet poles. At the ends I82) and 20b, the straps l8 and 20 extend outwardly in ears which receive the tightening screw 22, this screw passing freely through 3 strap and being threadedly received in strap I8.

If desired, the ears may be of shape other than shown in the drawing, provided they isolate the magnet 24 from the poles I8a and 29a and provide a space for the shunt 26.

The screw 22 is of non-magnetic material or, with proper choice of pole piece shape, may be magnetic.

Opposite the ears 18b and 201), the straps I8 and 20 extend in parallel relation away from the tube neck, this region being indicated at 18c and 200, thus defining a pair of faces contiguous with the arcuate portions 18a and 26a. Outboard of this region, the straps converge to a closer spacing at [811 and 20d where they are secured, by

welding or by suitable adhesive, to the opposite ends or poles of the permanent magnet 24.

The magnet 24 may be any one of the many permanent magnets available to the art. It is preferable, of course, to use a magnet with maximum stored energy.

In the space defined by the parallel spaced portions I 80 and 280 of the straps H3 and 26, the trap has a-magnetic shunt 28. It is the purpose of this shunt to make uniform the fiux density between the arcuate portions Mia and 23a of the trap. In the embodiment shown, this shunt is of spring steel and is adjustably disposed in this spacing and is held therein by the friction resulting from its own fiexure. Each end of the shunt 26 has an extending ear 26:! which fits in the mating slot I! of the corresponding strap, thus securing the shunt against being pushed out of the space between portions [30 and 250 of the straps.

The effect of the strap is-best shown in the diagram of Figure 3. This diagram shows the variation in flux density along the axis X-X, Figure 2, the lower part of the diagram corresponding to the lowermost reach of the bottom of the tube neck and the upper part of the diagram corresponding to the uppermost reach of the top of the tube neck. When the shunt 26 is properly positioned, the flux density in traversing line X--X is substantially constant and gives rise toeffective, non-critical ion trap action without loss of electron beam strength and without introducing defocusing.

When the shunt 26 is moved towards the neck of the tube, the flux varies as shown at curve A, Figure 3, so that the fiux density tapers off as the top of the neck of the tube is approached. If the shunt 2G is shifted too far from the neck of the tube, asshown by the dotted lines, Figure 2,

the flux varies as shown at curve E, Figure 3.

In this case the fiux density increases as the top of the tube neckis approached.

'Prior to use the ion trap is adjusted to give the uniform flux density curve of the solid line of Figure 3. This may be accomplished by factory adjustments, after which the shunt 26 is secured in position by a drop of solder or similar securing material. It may also be accomplished by adjustment after the ion trap is placed on the neck of the tube. In either event, the flux within the tube is made uniform and the trap can then be rotated relative to the tube neck and moved longitudinally on the tube neck until the most intense electron beam is observed.

It is believed that the linear fiux distribution along the axis X-X is due to action analogous to that of an electrical parallel circuit. The entire assembly, less the shunt, represents a series of distributed impedances, or in the magnetic case, reluctances, which change incrementally along the axis X-X as a function of the distance between the pole pieces, along the axis X-X, assuming that the width of the pole piece is held constant. In addition to this parallel reluctance, there is the series reluctance of the pole piece which causes a diminishing of magnetic energy as theend of the pole pieces isapproached.

By adding the shunt at the area shown, another circuit element is added in parallel. When the proper value of magnetic reluctance is chosen,

the magnetic circuit becomes magnetically constant as the reference point is moved along the axis In any event, it is possible by choosing the characteristics of the shunt to achieve a uniformfield.

The shunt 26 may be of any magnetic material, such as soft iron, steel, etc.

The shunt 26 may be secured in position in any convenient fashion. While it is considered preferable to mount the shunt so thatit can be moved easily to permit adjustment, this is not essential and the shunt can be fixed permanently in place at the time of manufacture.

The members It and 2B, which are shown as straps, need only be capable of acting as magnet poles and hence may be of any conformation defining the neck-receiving arcuate portions, the magnet receiving portions, and the shunt receiving faces.

While we have shown and described a particular embodiment of our invention, it will be understood that many modifications and alternative constructions canbe made without departingfrom the true spirit and scopeof our invention. We, therefore, intend to cover by the appended claims all modifications and alternative constructions coming within the truespirit and scope thereof.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. A magnetic device adapted to receive the neck of a cathode ray tube and characterized by a relatively uniform flux density comprising, a pair of complementary magnetic pole pieces 2 having arcuate portions adapted to straddle the neck of the tube and defining a pair of extending faces at corresponding ends and contiguous with the arcuate portions, the faces being fiat and having a substantial spacing, a magnet received by said pole pieces outboard of said faces to createmagnetic flux between said facesand between said arcuataportions, and a magnetic shunt extending between said faces and adjustably held thereby.

2. A magnetic device adapted toreceive the neck of a cathode ray tube and characterized by a relatively uniform flux density comprising, a pair of complementary magnetic pole pieces having arcuate portions adapted to straddle the neck of the tube and defining a pair of extending faces at corresponding ends and contiguous with the arcuate portions, a magnet'receiyedby said polepieces outboard of said faces tocreate magnetic flux between said faces and, between said arcuate portions, and a magnetic shunt extending between said faces and adjustably held thereby.

3. A magnetic device adapted to receive ,the

neck of a cathode raytube and characterized dle ,the ,neck, of. .the tube, and, defining a pair ,of'

extending faces at. corresponding ends and ,contiguous'with the arcuate portions, the faces being flat and having a substantial spacing, a magnet received by said pole pieces outboard of said faces to create magnetic flux between said faces and between said arcuate portions, and a magnetic shunt extending between said faces.

4. A magnetic device adapted to receive the neck of a. cathode ray tube and characterized by a relatively uniform flux density comprising, a pair of complementary magnetic pole pieces hav ing arcuate portions adapted to straddle the neck of the tube and defining a pair of extending faces at corresponding ends and contiguous with the arcuate portions, a magnet received by said pole pieces outboard of said faces to create magnetic flux between said faces and between said arcuate portions, and a magnetic shunt extending between said faces.

5. A magnetic device adapted to receive the neck of a cathode ray tube and characterized by a relatively uniform flux density comprising, a magnet havingv poles at its opposite ends, a pair of complementary magnetic pole pieces received on the opposite ends of the magnet, the pole pieces having arcuate portions adapted to receive the neck of the tube and located in spaced 6 relation to the magnet, the pole pieces defining a pair of spaced faces in the regions intermediate the magnet and the arcuate portions, and a magnetic shunt extending between said faces.

DONALD PAUL INGLE. SOL L. REICHES.

- REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,499,065 Heppner Feb. 28, 1950 2,500,455 Fisher Mar. 14, 1950 2,513,929 Gethmann July 1950 2,539,156 Ostreicher Jan. 23, 1951 2,542,924 Heppner Feb. 20, 1951 2,544,898 Obszarny et a1. Mar. 13, 1951 2,552,341 Mucher May 8, 1951 2,552,342 Mucher May 8, 1951 2,553,792 Smith et a1 May 22, 1951 2,569,325 Obert Sept. 25, 1951 2,569,517 De Leon Oct. 2, 1951 2,574,039 Ingle et a1. Nov. 6, 1951 

